All platforms: Mozilla's pushed out the latest release of the Firefox 3 beta for testers and impatient upgraders. Firefox 3 Beta 4 improvements include a better download manager, smarter location bar auto-complete, speedier performance (twice as fast using Google Apps, says Moz), better memory handling, and even more native look and feel for Mac, Windows, and Linux users with new icons and toolbars. After the jump, check out the Beta 4 highlights from the release notes.

New Download Manager: the revised download manager makes it much easier to locate downloaded files, and you can see and search on the name of the website where a file came from. Your active downloads and time remaining are always shown in the status bar as your files download.

Full page zoom: from the View menu and via keyboard shortcuts, the new zooming feature lets you zoom in and out of entire pages, scaling the layout, text and images, or optionally only the text size. Your settings will be remembered whenever you return to the site.

Integration with Vista: Firefox now has Vista-specific icons, and uses native user interface widgets in the browser and in web forms.

Integration with the Mac: the new Firefox theme makes toolbars, icons, and other user interface elements look like a native OS X application. Firefox also uses OS X widgets and spell-checker in web forms and supports Growl for notifications of completed downloads and available updates. A combined back and forward control make it even easier to move between web pages.

Integration with Linux: Firefox's default icons, buttons, and menu styles now use the native GTK theme.

Location bar & auto-complete: type in all or part of the title, tag or address of a page to see a list of matches from your history and bookmarks; a new display makes it easier to scan through the matching results and find that page you're looking for. Results are returned according to their frecency (a combination of frequency and recency of visits to that page) ensuring that you're seeing the most relevant matches. An adaptive learning algorithm further tunes the results to your patterns!

Speed: improvements to our JavaScript engine as well as profile guided optimizations have resulted in significant improvements in performance. Compared to Firefox 2, web applications like Google Mail and Zoho Office run twice as fast in Firefox 3 Beta 4, and the popular SunSpider test from Apple shows improvements over previous releases.

Memory usage: Several new technologies work together to reduce the amount of memory used by Firefox 3 Beta 4 over a web browsing session. Memory cycles are broken and collected by an automated cycle collector, a new memory allocator reduces fragmentation, hundreds of leaks have been fixed, and caching strategies have been tuned.

Firefox 3 Beta 4 is a free download for testers; it IS a beta so expect bugs and weirdness, and the possibility that not all of your extensions will work with it. (Here's a workaround for getting your extensions to work in the Firefox 3 Beta).